📖 Clarify storage class requirement for crypto.encryptionClassName API

[dilyar85]

What does this PR do, and why is it needed?

This PR updates the API doc for the crypto.encryptionClassName field to reflect the validation logic in the VM webhook, which requires an encrypted storage class when this field is set. It also adds a comment in the webhook code explaining why the error is returned on encryptionClassName even though the validation checks the storage class.

Which issue(s) is/are addressed by this PR?

Fixes N/A.

Are there any special notes for your reviewer:

We should probably return both fields in the validating webhook result once K8s supports combining field errors.

Please add a release note if necessary:

Clarify storage class requirement for crypto.encryptionClassName API

---

📚 Documentation preview 📚: https://vm-operator--747.org.readthedocs.build/en/747/

[github-actions]

Package	Line Rate	Health
github.com/vmware-tanzu/vm-operator/controllers/contentlibrary/clustercontentlibraryitem	82%	➖
github.com/vmware-tanzu/vm-operator/controllers/contentlibrary/contentlibraryitem	85%	➖
github.com/vmware-tanzu/vm-operator/controllers/contentlibrary/utils	97%	✔
github.com/vmware-tanzu/vm-operator/controllers/infra/capability/configmap	86%	➖
github.com/vmware-tanzu/vm-operator/controllers/infra/capability/crd	93%	✔
github.com/vmware-tanzu/vm-operator/controllers/infra/configmap	71%	❌
github.com/vmware-tanzu/vm-operator/controllers/infra/node	77%	❌
github.com/vmware-tanzu/vm-operator/controllers/infra/secret	77%	❌
github.com/vmware-tanzu/vm-operator/controllers/infra/validatingwebhookconfiguration	85%	➖
github.com/vmware-tanzu/vm-operator/controllers/infra/zone	76%	❌
github.com/vmware-tanzu/vm-operator/controllers/storageclass	94%	✔
github.com/vmware-tanzu/vm-operator/controllers/storagepolicyquota	97%	✔
github.com/vmware-tanzu/vm-operator/controllers/util/encoding	73%	❌
github.com/vmware-tanzu/vm-operator/controllers/virtualmachine/storagepolicyusage	99%	✔
github.com/vmware-tanzu/vm-operator/controllers/virtualmachine/virtualmachine	86%	➖
github.com/vmware-tanzu/vm-operator/controllers/virtualmachine/volume	86%	➖
github.com/vmware-tanzu/vm-operator/controllers/virtualmachineclass	75%	❌
github.com/vmware-tanzu/vm-operator/controllers/virtualmachinepublishrequest	81%	➖
github.com/vmware-tanzu/vm-operator/controllers/virtualmachinereplicaset	68%	❌
github.com/vmware-tanzu/vm-operator/controllers/virtualmachineservice	83%	➖
github.com/vmware-tanzu/vm-operator/controllers/virtualmachineservice/providers	92%	✔
github.com/vmware-tanzu/vm-operator/controllers/virtualmachinesetresourcepolicy	80%	➖
github.com/vmware-tanzu/vm-operator/controllers/virtualmachinewebconsolerequest/v1alpha1	72%	❌
github.com/vmware-tanzu/vm-operator/controllers/virtualmachinewebconsolerequest/v1alpha1/conditions	88%	➖
github.com/vmware-tanzu/vm-operator/controllers/virtualmachinewebconsolerequest/v1alpha1/patch	78%	❌
github.com/vmware-tanzu/vm-operator/controllers/virtualmachinewebconsolerequest/v1alpha2	73%	❌
github.com/vmware-tanzu/vm-operator/pkg/bitmask	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/builder	95%	✔
github.com/vmware-tanzu/vm-operator/pkg/conditions	88%	➖
github.com/vmware-tanzu/vm-operator/pkg/config	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/config/capabilities	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/config/env	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/context/generic	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/context/operation	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/patch	78%	❌
github.com/vmware-tanzu/vm-operator/pkg/prober	91%	✔
github.com/vmware-tanzu/vm-operator/pkg/prober/probe	90%	✔
github.com/vmware-tanzu/vm-operator/pkg/prober/worker	77%	❌
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere	75%	❌
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/client	80%	➖
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/clustermodules	71%	❌
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/config	89%	✔
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/contentlibrary	74%	❌
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/credentials	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/network	80%	➖
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/placement	79%	❌
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/session	71%	❌
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/storage	44%	❌
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/sysprep	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/vcenter	82%	➖
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/virtualmachine	84%	➖
github.com/vmware-tanzu/vm-operator/pkg/providers/vsphere/vmlifecycle	67%	❌
github.com/vmware-tanzu/vm-operator/pkg/record	78%	❌
github.com/vmware-tanzu/vm-operator/pkg/topology	91%	✔
github.com/vmware-tanzu/vm-operator/pkg/util	87%	➖
github.com/vmware-tanzu/vm-operator/pkg/util/annotations	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/cloudinit	89%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/cloudinit/validate	91%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/image	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/kube	87%	➖
github.com/vmware-tanzu/vm-operator/pkg/util/kube/cource	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/kube/internal	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/kube/spq	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/paused	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/ptr	100%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/resize	97%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/vmopv1	92%	✔
github.com/vmware-tanzu/vm-operator/pkg/util/vsphere/client	64%	❌
github.com/vmware-tanzu/vm-operator/pkg/util/vsphere/vm	79%	❌
github.com/vmware-tanzu/vm-operator/pkg/util/vsphere/watcher	86%	➖
github.com/vmware-tanzu/vm-operator/pkg/vmconfig	95%	✔
github.com/vmware-tanzu/vm-operator/pkg/vmconfig/crypto	98%	✔
github.com/vmware-tanzu/vm-operator/pkg/webconsolevalidation	100%	✔
github.com/vmware-tanzu/vm-operator/services/vm-watcher	91%	✔
github.com/vmware-tanzu/vm-operator/webhooks/common	100%	✔
github.com/vmware-tanzu/vm-operator/webhooks/persistentvolumeclaim/validation	95%	✔
github.com/vmware-tanzu/vm-operator/webhooks/unifiedstoragequota/validation	92%	✔
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachine/mutation	87%	➖
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachine/validation	95%	✔
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachineclass/mutation	62%	❌
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachineclass/validation	89%	➖
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachinepublishrequest/validation	92%	✔
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachinereplicaset/validation	90%	✔
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachineservice/mutation	67%	❌
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachineservice/validation	92%	✔
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachinesetresourcepolicy/validation	89%	✔
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachinewebconsolerequest/v1alpha1/validation	92%	✔
github.com/vmware-tanzu/vm-operator/webhooks/virtualmachinewebconsolerequest/v1alpha2/validation	92%	✔
Summary	83% (10342 / 12453)	➖

Minimum allowed line rate is 79%

[akutz]

Lgtm @dilyar85 , thank you!